The subject matter of the present invention is additives for mineral binders, based on a composition containing at least one product of internal dehydration of a hydrogenated sugar. The subject matter is also mineral binders with additives and the use of said additives or said compositions for the preparation of mineral binders.
By xe2x80x9cmineral binderxe2x80x9d is meant, in the sense of the present invention, any hydraulic binder, especially any mineral powder, capable of forming with water a paste, setting and hardening progressively even when sheltered from air. Usually, at ambient temperature, a mineral binder begins to form with water such a paste in a time span of roughly several minutes to less than 48 hours, generally between roughly 30 minutes and 24 hours. This definition is applied, amongst other things, to cements, to natural or artificial hydraulic limes, but also to mixtures, pasty or hardened, such as mortars, grouts, coatings and concretes, based on crushed cement and/or limes, water and/or aggregates (sands, gravels, pebbles . . . ), and finally to the raw materials going into the manufacture of cements such as pozzolanic cement, clinker cement, slag cement, calcareous fillers and silica fumes. By xe2x80x9cmineral binderxe2x80x9d is meant also any non-hydraulic binder based on calcium sulphate, gypsum and/or lime.
Depending on their final usages and conditions of use, it is sometimes necessary to add to mineral binders additives such as grinding agents or crushing aids, accelerators for setting and/or hardening, retarders of setting, plasticisers, water-reducing agents/plasticisers, superplasticisers and thickeners. These additives make it possible, for example, to modify the fluidity, pumpability, handling, setting, hardening, strength, durability and/or certain other properties of the mineral binder.
Numerous sugars and derivatives are already used in the preparation of additives for mineral binders, including:
molasses, which are inexpensive products, used as plasticisers;
sugars, which are very good plasticising water-reducing agents but strongly delay setting;
oxidised sugars, very good plasticising water-reducing agents, retarding agents for setting and which also make it possible to improve strength at 28 days as described in the patents FR 2 387 194 and GB 1 508 761;
hydrogenated sugars, which are plasticisers/water-reducing agents as described in the patent FR 2 726.550, but which are lesser retarding agents than the oxidised sugars whilst improving strength at 28 days, as results from the American patent U.S. Pat. No. 4,073,658;
hydrogenated or oxidised sugar syrups which are also described as grinding agents, according to patent EP 0 696 557;
esters of higher fatty acids and of polyols such as sorbitan trioleate which are agents for controlling the capacity for absorbing water and agents for improving the resistance to water and the adherence of cement compositions in the hardened state as described in the Japanese patent JP 59121143. These esters of higher fatty acids appear, moreover, to be retarders of setting and/or hardening.
Currently, for the preparation of cements, the tendency is to use products which are less expensive than clinker and/or to reduce the use of the latter. However, clinker provides good strength at 28 days. There exists therefore a need for an additive making it possible to correct the strength at 28 days of cements which do not contain clinker or contain little clinker.
Moreover, as regards mortars, grouts and concretes, the industry is searching for new accelerators of setting and/or hardening.
The setting and/or hardening accelerators conventionally used up till present are, on the one hand chlorinated products such as for example calcium chloride, and on the other hand non-chlorinated products, strongly acid or basic, such as for example respectively formic or sulphuric acids, their salts, lime, soda or products deriving therefrom (sodium metasilicates or aluminates).
Such accelerators are currently used particularly during the preparation of mineral binders intended to be used at low temperatures, i.e. at temperatures lower than roughly 15xc2x0 C., or during the realisation in the factory of prefabricated articles.
However, the chlorinated products have the major drawbacks of being corrosive vis-à-vis enclosures for preparing the binders and the metal reinforcements utilised within the concretes used in civil engineering or the construction of buildings and of being a source of chlorine, a product known to be harmful to the environment.
For their part, the strongly acid or basic products present the drawbacks of being corrosive vis-à-vis metals and aggressive vis-à-vis the skin and the eyes and of not always making it possible to obtain sufficiently improved strengths when fresh and/or at 28 days.
Neutral and non-chlorinated products are sometimes used as accelerators of setting and/or hardening, such as lithium carbonate for example. However this compound has the drawback of being expensive in relation to the above-mentioned products.
Moreover, it has the tendency to reduce significantly the plasticity of the mineral binders and to be weakly effective at low temperatures.
There exists therefore a need to be able to have available an additive for mineral binders which, simultaneously:
is ecological, inoffensive during its use and non-corrosive vis-à-vis metals,
is an accelerator of setting and/or hardening and makes it possible consequently to obtain improved strengths when fresh, sufficient to make possible rapid dismantling of formwork and this as much at ordinary temperatures as at low temperatures,
confers a correct plasticity, if possible improved, to the mineral binders when they are used, and
then confers to these binders mechanical properties at 28 days which are correct and if possible improved.
Within the framework of the present invention, what is meant by plasticity of the mineral binder is the capacity to obtain a Theological state in which the mineral binder can be handled, poured or pumped. The plasticity is measured according to the standardised method CEN 196-01, by which one measures in mm the spread of a given volume of mineral binder on a shock table.
The start and end of setting are measured with the aid of an automatic xe2x80x9cprisomxc3xa8trexe2x80x9d with the trademark xe2x80x9cACMELxe2x80x9d.
The mechanical strength when fresh is measured on specimens of mineral binder according to the standard CEN 196-01, quoted above, and this 17 or 24 hours after the manufacture of the specimens. This mechanical strength when fresh should, in general be greater than 5 Mpa to permit dismantling of the formwork. Moreover, the strength over time of the mineral binders (for example at 3 or 28 days) is also measured according to the above-quoted standard CEN 196-01.
The applicant company has had the merit of finding, after extensive research, that an additive meeting the above-quoted requirements of current technology could consist in a particular composition containing a selected sugar derivative.
In a more precise manner, the subject matter of the present invention is a new additive for mineral binders characterised in that it comprises a composition containing at least one product of internal dehydration of a hydrogenated sugar. In a surprising and unexpected manner, such dehydration products behave in a totally different manner from the hydrogenated sugars from which they are derived and which are known as being retarding agents as recalled above.
By xe2x80x9cproduct of internal dehydrationxe2x80x9d is meant any product resulting, in any manner whatsoever, in one or several stages, from the removal of one or more molecules of water at the level of the original internal structure of a hydrogenated sugar and any compound containing, as a result especially of possible (poly)condensation phenomena, such a product. What is also meant is any compound resulting from the chemical modification and for example from the etherification of such a product or its esterification by a non-fatty chain. Such compounds can consist especially of acetylated, ethylated, methylated, propylated, butylated, ethylenated, propylenated derivatives of isosorbide or isomannide. It can also be in particular dimethyl isosorbide.
Preferably the hydrogenated sugar is a hydrogenated monosaccharide, especially chosen from hexitols, pentitols, tetritols, and their mixtures. It can also be a hydrogenated di-, oligo- or polysaccharide or any mixture of these products.
According to a particularly advantageous variant, the dehydration product stems from the internal dehydration, more or less forced, of a hexitol such as sorbitol, mannitol or galactitol for example and consists especially in a dehydrated hexitol chosen from isosorbide, isomannide, sorbitan, mannitan and any mixtures of at least any two of these products.
According to another variant, the composition contained in the additive according to the invention has a content of dehydration product(s) of at least 5%, preferably at least 10%, and more preferably at least 40%, these percentages being expressed in total dry weight of dehydration product(s) in relation to the dry weight of said composition.
The Applicant Company has found, as will be exemplified below, that compositions which have a total content of isosorbide and sorbitan of at least 15%, preferably of at least 55%, and more preferably still of at least 70%, were of particular interest as agents accelerating setting and/or hardening of mineral binders or as agents improving the mechanical properties of these binders.
And it is worth emphasising that such unexpected properties can be obtained:
for introduction rates in these compositions within the mineral binders, generally lower than the standard setting and/or hardening accelerators quoted previously, and
just as well at ordinary temperatures, i.e. equal to or greater than roughly 15xc2x0 C., as at low temperatures.
The subject matter of the present invention is also a mineral binder characterised in that it contains between roughly 0.001 and 5%, preferably between 0.01 and 2%, of an additive such as described above, these percentages being expressed in dry weight of the said additive in relation to the total dry weight of raw material(s) for cement, of cement and/or of lime contained in said mineral binder.
Contents of additive of the order of 0.1 to 1% can generally suit all mineral binders and all conditions, including of temperature, of their being placed and their hardening.
The additive according to the invention can be, or not be, constituted entirely of the composition based on the product(s) of dehydration described above.
In this case, the said composition can present itself in liquid, pasty or solid form.
The non-solid forms can have a very large range of dry matter (MS) for example an MS of between roughly 30 and 85%.
The proportion of dehydration product(s) such as described below in relation to the total dry matter of this composition, can also vary greatly as already explained.
These amounts and proportions of dry matter depend especially on the method of obtaining said composition. By way of non-restrictive example, this composition can consist:
in a reaction medium which is not purified, designated below xe2x80x9cPRODUCT Axe2x80x9d, stemming from the standard dehydration of sorbitol under the effect of an acid and of the temperature, this medium having a dry matter of roughly 50% and a total content of isosorbide+sorbitan of roughly 75% (dry/dry),
in a crystallised isosorbide powder of very high purity (purity=99%), designated below xe2x80x9cPRODUCT Bxe2x80x9d, coming from the direct distillation of PRODUCT A,
in the residue of distillation obtained jointly with PRODUCT B, hereinafter designated xe2x80x9cPRODUCT Cxe2x80x9d, having a dry matter of roughly 58% and a total content of isosorbide+sorbitan of roughly 19% (dry/dry),
in a PRODUCT A enriched with isosorbide and sorbitan, hereinafter designated xe2x80x9cPRODUCT Dxe2x80x9d, having a dry matter of roughly 79% and a total content of isosorbide+sorbitan of roughly 89% (dry/dry),
in an enriched medium stemming from a double distillation of PRODUCT D, hereinafter designated xe2x80x9cPRODUCT Exe2x80x9d, having a dry matter of roughly 83% and a total content of isosorbide+sorbitan of roughly 99%,
in the residue of said double distillation such as obtained jointly with PRODUCT E, hereinafter designated xe2x80x9cPRODUCT Fxe2x80x9d, this residue having a dry matter of roughly 42% and a total content of isosorbide+sorbitan of roughly 89%,
in pulverulent sorbitan of a purity of roughly 95%, hereinafter designated xe2x80x9cPRODUCT Gxe2x80x9d, and
in pulverulent isomannide, of a purity of roughly 95%, hereinafter designated xe2x80x9cPRODUCT Hxe2x80x9d.
Such compositions, usable according to the invention, can have a pH within a wide range and in particular between roughly 2.5 and 6.5.
The additive according to the invention can also contain, apart from said composition, one or more additives traditionally used for the preparation of mineral binders, including at least one standard setting and/or hardening accelerator such as those quoted above.
The Applicant noted especially that it could be advantageous to associate a product of internal dehydration of a hydrogenated sugar such as isosorbide with lime or with sodium sulphate.
The additive thus obtained can also present itself in liquid, pasty or solid form.
Generally speaking, the additive according to the invention, constituted or not of the sole composition based on product(s) of internal dehydration of hydrogenated sugar(s), is completely appropriate for being used as an additive for cement and this before, during and/or after crushing, or as an additive for hydraulic limes. It is also completely appropriate for being used as an additive for concretes, grouts and mortars, whether they are liquid or solid.
The additive according to the invention can be introduced into the mineral binders according to a multitude of different ways. It can be introduced entirely during a particular stage of manufacture, storage, adding the additive, transport or placing of the mineral binder or in a divided manner during several of these particular stages. It can, for example, be used, completely or partially, during the manufacture of pulverulent mineral binders, including at the level of cement works, before, during and/or after crushing or during the preparation of dry and/or ready-to-use mortars or concretes. It can also be used, totally or partially, during transport of pasty or liquid mineral binders, or during their manufacture in the factory or on site, and for example in the mixing water and/or the necessary aggregates for preparation, notably in enclosures commonly called concrete batching and mixing plants.
As a result of which, the subject matter of the present invention is also respectively:
the use of such an additive for the preparation of a mineral binder, and
the use of a composition containing at least one product of internal dehydration of a hydrogenated sugar, in particular of a dehydrated hexitol, for the preparation of such an additive or of a mineral binder.
The general concept of the present invention rests equally on the surprising and unexpected use of such a composition, on its own or within a more complex additive as:
an accelerating agent for setting and/or hardening of a mineral binder and/or
an agent for improving the mechanical properties of a mineral binder in the hardened state.
And it is remarkable to note, as already emphasised, that such advantageous functionalities are expressed just as well at ordinary temperatures as at low temperatures.